H264: VFR to CFR without re-encoding - possible?

[rgr]

Is there a way to convert VFR (28-30fps) to CFR (30fps) without re-encoding? From what I see, ffmpeg does not have this option, VDub2 also refuses with the H264 codec.
(Audio doesn't matter)

[ProWo]

Use the newest beta of clever Ffmpeg-GUI.
Load your file, click main, click various, click change framerate.
It changes the videostream only.
audiostreams have to be adapted separately.
works with x264 and hevc only.

You can also try the fix timestamps option first.
this one works for the whole video.

[rgr]

Thanks, worked

[jagabo]

Be careful. Converting VFR to CFR by that method can lead to audio and video being out of sync. Say for example you have a 2000 frame video where the first half is all 28 fps, and the second half is all 30 fps. The first 1000 frames will play for ~35.7 seconds (1000/28), the second half will follow for 33.3 seconds (1000/30). If you convert to an average of 29 fps the first 1000 frames will play in ~34.5 seconds (1000/29). Then the second half of the video will play for another 34.5 seconds (1000/29). So even though both videos play for the same total time, and the audio is in sync at the start and end, the audio will be out of sync by a about 1.2 seconds in the middle.

[rgr]

Be careful. Converting VFR to CFR by that method can lead to audio and video being out of sync.

The video has no sound, so there will be no problem

However, I thought that a knowledgeable person could easily write a script that gives the deviation for each frame (or just the maximum deviation) from the average fps for such a CFR-converted clip.

[Cornucopia]

No, @rgr, there is still the probability that motion is not consistent with the original. Iow, depending on the type of motion in the scene or camera, there can be added jerkiness. That is what @jagabo referred to.


Scott

[rgr]

No, @rgr, there is still the probability that motion is not consistent with the original. Iow, depending on the type of motion in the scene or camera, there can be added jerkiness. That is what @jagabo referred to.


Scott

Yes, but I see that the fluctuations are slight.


Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 30.000 FPS
Minimum frame rate : 27.907 FPS
Maximum frame rate : 43.103 FPS

[butterw]

Avidemux journal contains the frame duration histogram: https://avidemux.org/smif/index.php?topic=19536.0
If the video is detected as VFR because of jitter/rounding error, it is safe to convert to CFR and indeed Avidemux does this automatically when remuxing.
Anything else is inherently risky, though it might still work.